instmctions): The Mouse Model Core (Core A) is an established Core facility of the Program Project that has the overall goal to enhance the research endeavors of the Units and facilitate the conduct of research by individual Research Units that require support for conducting experiments involving mice, and in mouse breeding and maintenance. The Core offers the following high-quality services in a cost-effective manner to Program investigators: 1. Breeding and maintenance of normal and mutant mice a. Acquisition and basic maintenance of normal and mutant mouse strains b. Design and implementation of breeding schemes involving normal and mutant mice c. Assistance in generating new mutant mice 2. Assistance in conducting mouse experiments a. Infections with enteric pathogens b. Induction and analysis of experimental colitis models c. Irradiation and bone marrow transplantation d. Collection of tissues, blood and fecal samples e. Preparation and use of ligated intestinal loops 3. Administrative and training support for mouse studies a. Administrative assistance in acquiring and transferring animals b. Support in preparation and submission of animal protocols, and compliance procedures c. Training in conducting animal studies The Mouse Model Core is fully equipped and has an experienced animal technician to provide the offered services at the highest quality in a cost-effective manner. The Core interacts closely with individual Program investigators and the other Cores to assist in achieving the scientific objectives of the Program. RELEVANCE (See instmctions): Animal models are critical for immunological research because the complexity of the immune system can only be adequately investigated in the normal biological context. Mice are the preferred model for the studies, since they are genetically closely related to humans, are readily amenable to different experimental designs, and many genetically engineered strains and immunological reagents are commonly available.